1. Field of the Invention
This invention relates to a hole enlargement arrangement and method of use.
2. Description of the Prior Art
Various types of hole enlargement arrangements have been heretofore employed and are currently in use. In the devices with which applicant is familiar, a body structure formed of inner and outer body sections has cutter arms pivotally secured on the outer body section and a piston and cylinder means defined between the inner and outer body sections receive hydraulic fluid to effect telescopic movement of the body sections in one relative direction whereupon a cam surface mechanically engages and forces the cutter arms out to underreaming or bore hole enlarging position.
After the underreaming operation is completed, the cutter arms of the prior art devices are generally then retracted by raising the operating string on which the body structure is supported so that the expanded or projecting arms engage the shoulder formed at the juncture of the upper end of the enlarged underreamed portion with the smaller bore. Continued raising of the operating string exerts a force on the extended cutter arms to endeavor to force the arms inwardly to retracted position relative to the body structure.
If mud or some other obstruction prevents relative longitudinal telescopic movement between the inner and outer body sections so that the cutter arms can retract, then it has been generally customary in such circumstances to merely continue exerting a pull on the operating string until some portion of the bore hole enlarging structure breaks so that it then may be withdrawn from the well bore. Also, it can be appreciated that if the structure of the prior art malfunctions or breaks so that the inner and outer bodies are locked against telescopic movement while the arms are in extended position, then the arms again are forced to collapsed position by pulling up on the operating string to try to force them to retracted position, or to break whatever structure may be necessary to enable the prior art bore hole enlarging arrangement to be withdrawn from the bore hole.
When the arms of the bore hole enlarger are extended during drilling operations to underream or drill an enlarged portion in a bore hole, there are various forces that act upon the cutter arms during the bore hole enlarging operations. Some of such forces include an upwardly directed force on the outer projecting end of the arm due to the reaction from the weight of the operating string during drilling operations. There also are other forces. For example, there is a force which tends to move the cutter arms back towards retracted position due to the angle of the hole, a force due to the reaction from rotation while drilling the formation which tends to retract the cutter arms inwardly, and a force which arises from rotation during bore hole enlarging operations so that formation pressure against the leading edge of the arm along its axial extent tends to flex the cutter arm.
In prior art devices, these forces are transmitted from the cutter arms to the pivot arrangement of the cutter arms on the body structure and cam surface relied upon to move and maintain the cutter arms in extended cutting position. In some circumstances these forces may be substantial and in some instances damage or break components of the bore hole enlarger.
The present invention provides an arrangement that assists in overcoming the above and other problems. The cutter arms are pivotally mounted on the inner body structure and a cooperative support arrangement on the outer body section and cutter arms is employed to assist in moving or expanding the cutter arms to expanded cutter position and to assist in retracting the arms when the cutting operation is over. The cooperating support arrangement also assists in better distributing the loads and forces employed during the bore hole enlarging operation and also increases the mechanical advantage tending to maintain the cutter arms in expanded position during bore hole enlarging operations.